heating and cooling loads

QUESTION 1 The BCA defines the following terms. With the aid of a diagram describe their meanings:

- Envelope - Conditioned space - Non-conditioned space

QUESTION 2 According to the BCA, and with the aid of diagrams explain:

- Conduction through glazing - Radiant heat gain through glazing

QUESTION 3 Describe with the aid of diagrams the following mechanisms of heat transfer:

1) Natural convection 2) Forced convection 3) Conduction 4) Radiation

QUESTION 4 Why is it important to be able to locate the position of the Sun relative to points on the Earth’s surface when calculating heat loads on buildings? Describe with the aid of diagrams the following quantities associated with solar geometry and solar energy striking a surface:

1) Solar azimuth angle 2) Solar zenith angle 3) Solar hour angle 4) Surface azimuth angle 5) Angle of incidence of direct solar radiation on a surface.

QUESTION 5 The temperature, sT , of a surface subjected to solar radiation can be determined by solving the following heat balance equation

( ) ( ) ( ) ( )

( ) ( ) ( ) ( ) 0 2

cos1 2

cos1 2

cos1 2

cos1 cos

44

44

=−−−− −

−−

+ −−

+ +

− +

insidesambients p

grounds

p skys

p diff

p glohorizidir

TT d kTThTT

TTIII

θ εσ

θ εσ

θ α

θ ραθα

in which the symbols have meanings that are intuitive to students of the subject. Describe, with diagrams, the meanings of each of the seven groups of terms in the equation. Outline how you would use the Newton-Raphson method to solve the equation for sT given that all of the other values of the variables are known. QUESTION 6 Describe the key ideas used to derive the following expression for the rate of heat flow, Q, through glazing

( )io oi

i TTU hh IhIQ −+

+ +=

ατ

in which the symbols are ascribed the following meanings: Q = rate of heat transfer through the window, W/m2

τ = transmitivity of solar radiation through the glass α = absorptivity of solar radiation by the glass hi = heat transfer coefficient on inner surface of the glass, W/(m2.°C) ho = heat transfer coefficient on outer surface of the glass, W/(m2.°C) U = overall heat transfer coefficient across the glazing, W/(m2.°C) I = intensity of solar radiation incident on the glass, W/m2 To = temperature of the air on the outside of the window, °C Ti = temperature of the air on the inside of the window, °C Describe with the aid of a numerical example illustrate the effects of using tinted glass on the rate at which heat flows through windows, i.e. the transmitivity is reduced and the absorptivity is increased.